Centrifugal type separator



Nov. 29, 1966 K. PlNs ETAL 3,288,286

CENTRIFUGAL TYPE SEPARATOR Filed Feb. 18, 1964 5 Sheets-Sheet l if! E iii i E INVENTORS KLAAS PRINS 8 HAROLD DUNFEE d BY MAHONEY, MILLER 23 RAMBO ATTORNEYS Nov. 29, 1966 KY. PRINS ETAL 3,288,286

CENTRIFUGAL TYPE SEPARATOR Filed Feb. 18, 1964 5 Sheets-Sheet 2 I 0'71 I I f IIH l I I [Al I I III] MI I l I I IHI /7 m r HM i i 5 I 1 F i INVENTORS KLAAS PR/NS a HAROLD DUNFEE B MAHgC IEY, MILLER 8 RAMBO ATTORNEYS N 1966 K. PRINS ETAL 3,288,286

CENTRIFUGAL TYPE SEPARATOR Filed Feb. 18, 1964 5 sheetssheet 5 INVENTORS KL AAS PR/NS &

BY HAROLD DUNFEE MAHONEY, MILLER 8 RAMBO ATTORNEYS United States Patent Ofiice Patented Nov. 29, 1966 3,288,286 CENTRHUGAL TYRE SEPARATOR Klaas Prins, 104 E. D St., Wellston, Ohio, and Harold Dunfee, Wellston, Ohio Filed Feb. 18, 1964, Ser. No. 345,706 8 Claims. (Cl. 209211) Our invention relates to an apparatus for separating and classifying fragmentary materials of different specific gravities. In the following description we will refer to the separation and classification of the fragmentary impurities associated with coal fragments or particles which are usually of a higher density and higher specific gravity as compared to the coal particles, but it is to be understood that our invention is applicable to other materials.

Separation of impurities from coal is known by the trade as coal cleaning. Coal cleaning is upgrading of the coal output of the mine resulting in a more readily salable product with higher heat value or more B.t.u. The removal of the higher density material, such as shale, rock and heavy particles, is essential because these impurities impair the quality of the coal and lower its heat value.

Many processes have been developed and are in use today for cleaning coal. Among the more recent developments are the so-called heavy media processes in which a media is created to aid in separating the impurities and consists of finely divided solids in water to produce a suspension which is self-sustaining under moderate agitation. This media will allow the impurities of the coal mixture that is supplied to the media to co-mix in the suspension and the coal particles, which are of a lighter specific gravity, to float in the media. A detailed explanation of the removal of the various material fractions according to this heavy media process is not necessary; however, it is sufficient to point out that it is essential to remove from the coal and its impurities, the finely divided expensive media-producing solids of high specific gravity, which usually consists of magnetite, because the inclusion of this material with the coal and impurities would impair the burning quality of the coal and also would result in the loss of the magnetite which would make such a process prohibitive when considering the cost of the magnetite, especially when cleaning small particle coal consisting of particle or fragmentary materials of A maximum size.

With our apparatus, it is possible to clean the coal by utilizing centrifugal force and gravity in connection with a media which is created solely from the coal and impurities mixture that is supplied to the apparatus for cleaning without the addition of extraneous high specific gravity particles, such as magnetite. Also, the coal mixture to be cleaned is subjected in our apparatus to certain directional currents which facilitate separation of the impurities and the apparatus is so arranged as to obtain maximum efliciency in the use of these currents and in the use of centrifugal force and gravity to obtain effective separation and classification of the materials of the coal mixture.

More specifically, according to our invention, the coal mixture and water under pressure is supplied to a separating chamber in a separator that is mainly of inverted conical form. The pressure is suificient to produce a circular downward spiralling motion along the converging wall of the chamber with considerable centrifugal force. This centrifugal force is utilized to cause the materials to move outwardly toward the surrounding wall of the separator chamber and to bring most of the particles into close contact with each other and, as such, create a mobile bed of materials which is moving essentially in a downward direction. The thickness of this bed of particles increases in proportion to the extent of downward convergence of the inverted cone section as the bed moves downwardly along the wall thereof. Since this downwardly moving bed is subjected continuously to the centrifugal force and the impurities of this bed are of higher density, these impurities, according to the wellknown laws of gravity, are outermost and take a position in close contact with the downwardly converging wall of the separator chamber. Also, due to centrifugal force, the coal particles, consisting of the lower density materials, arrange themselves radially inwardly of the higher density impurity materials at the inner side of the bed away from the wall of the chamber. At the lower end of the chamber the separated impurities pass through an outlet passage which is a continuation of the chamber but before the coal particles reach that passage they are deflected upwardly and drawn upwardly through a passage which extends upwardly through the center of the inverted conical separator.

To avoid inclusion of impurities with the clean coal, a portion of the coal particles is usually permitted to move downwardly with the impurities of the bed into the outlet passage. This coal is removed from the impurities in a final separator which we preferably provide according to our invention. This final separator is, in essence, of the general structure as the primary separator and has the same general principle of operation.

In the accompanying drawings we have illustrated a oreferred embodiment of an apparatus capable of carry- Zng out the separation and classification process according to our invention.

In these drawings:

FIGURE 1 is a vertical sectional view taken through the apparatus.

FIGURE 2 is a fragmentary side elevational view taken along line 22 of FIGURE 1 showing the inlet and outlet of the primary separator.

FIGURE 3 is a horizontal sectional view taken along line 3-3 of FIGURE 1 through the primary separator.

FIGURE 4 is a horizontal sectional view taken along line 4-4 of FIGURE 1 through the primary separator.

FIGURE 5 is a horizontal sectional view taken along line 5-5 of FIGURE 1 through the final separator.

FIGURE 6 is a horizontal sectional view taken along 'line 66 of FIGURE 1 through the final separator.

FIGURE 7 is a horizontal sectional view taken along line 7-7 of FIGURE 1 through the final separator and through the connecting refuse outlet passage of the primary separator which leads into the final separator.

FIGURE 8 is a horizontal sectional view through the final separator taken along line 88 of FIGURE 1.

With reference to the drawings and specifically to FIGURE 1, we have illustrated one example of apparatus which may be used in carrying out a separation process according to our invention. The apparatus is shown as comprising generally a primary separator 11 and a final separator 12. The primary separator 11 has an upper inlet 13 for the coal mixture to be cleaned and an outlet passage or conduit 14 leading from the lower end thereof which is connected to the final separator 12. As will later appear, this outlet passageway 14 will supply a mixture of impurities and some coal particles to the final separator 12 for further separation. If desired, several primary separators 11 may be connected to a single final separator 12.

The primary separator 11 includes a lower inverted frusto-conical casing or housing section 15 which may be made of two halves of semi-circular cross section joined together along vertical joints by clamping bolts 16 (FIG- URE 2). Mounted on the upper end of this section 15 is a cylindrical or tubular casing or housing section 17 which has a flanged lower edge resting on a flanged upper edge of the section 15 and being clamped thereto by clamping bolts 18. Similarly mounted on the upper end of the section 17 is a supporting disc 19 held in place by means of clamsping bolts 20. This disc supports standards 21 which may carry driving mechanism (not shown) for a depending drive shaft 22 which extends downwardly through a packing gland 23 that is carried by the disc 19.

The lower end of the shaft 22 has mounted thereon an impeller 25 of a centrifugal pump which is illustrated in FIGURES 1 and 3. The impeller preferably comprises an upper disc 26 and a lower disc 27, the latter having a central suction inlet 28. Between the discs, the impeller blades 21 are disposed in upright position. These blades are curved and extend inwardly from the peripheral edges of the discs over the opening 28. Carried by the lower disc 27 around .the opening 28 and depending therefrom is a suction pipe or tube 30 which will rotate with the disc. It will be noted that the impeller 25 is disposed in the upper end of the cylindrical housing section 17 and that the suction tube 30 extends downwardly through that section and through the conical housing section 15.

The lower end of the suction tube 30 carries a collar 31 which is threaded thereon for vertical adjustment. The extreme lower edge of this collar 31 is associated with and cooperates with a deflector ring or lip 32 which has an upper angular deflector surface for deflecting material upwardly into the lower end of the tube. This material, as will later appear, will be material sliding down the wall of the separator chamber 35 which surrounds the tube 30, which is of annular cross section, and which is of gradually decreasing cross section because of the wall of the inverted frusto-conical housing 15 converging downwardly with the tube 30. At the extreme lower and narrow end of the housing section 15 an outlet is provided which communicates with the outlet passageway or conduit 14, previously mentioned, that forms a continuation thereof, the passageway being of the same cross-sectional diameter. This conduit 14 has a flange that is bolted by bolts 36 (FIGURE 7) to the flanged lower edge of the housing section 15.

As previously indicated, the inlet 13 is provided for supplying the coal and impurities mixture to the upper end of the primary separator 11. This mixture, with water, is supplied under pressure. The inlet 13 leads tangentially (FIGURE 4) into the cylindrical housing section 17 so that the mixture will be caused to swirl therein. The housing section 17 is also provided with an outlet passage 37 which leads tangentially from the impeller 25 (FIGURE 3) for discharging of the cleaned coal particles.

It will be noted from FIGURE 2 that this outlet 37 is at a higher level than the inlet 13.

The operation of the primary separator will be evident from FIGURE 1 wherein the flow of material is illustrated schematically. The coal with impurities, mixed in water, will flow preferably from an elevated tank (not shown) into the inflow pipe with preselected pressure.

The inflow velocity at the inlet 13 is sufiicient to produce a circular downward spiraling motion, through the separation chamber 35, which also creates centrifugal force. This centrifugal force will cause the particles in the mixture to move outwardly toward the peripheral wall of the enclosing cylinder 17 and inverted cone section 15. Most of the particles will be brought into close contact with each other and as such create a mobile annular bed of particles of material which is moving essentially in a downward direction. The thickness of this bed of particles gradually increases downwardly in proportion to the decrease in cross-sectional area of the inverted cone section. Since this bed is continuously subjected to centrifugal force and since the impurities are of a higher density, these impurities, according to the well-known laws of gravity, take a position in lose contact with the peripheral wall of the chamber 35. The coal particles, consisting of the lower density materials, arrange themselves inwardly of the higher density impurity particles. When this bed of material passes through the annular restricted space,

between the outer wall of the chamber 35 and the end of the rotating suction tube 39 carried by the centrifugal pump impeller 25, the coal particles are caught in the current created by the pump and are drawn upwardly through the suction tube 341, the pump, and discharge outwardly through the tangential discharge outlet 37. The action of the pump in withdrawing the coal particles is enhanced by the deflector ring which provides an inwardly directed deflector lip 32 that will cause a retarding action on the downwardly moving bed of materials, simu1taneously directing the low density coal particles toward the intake or suction tube 30 of the rotating impeller 25.

To avoid inclusion of impurities with the cleaned coal drawn upwardly through the suction tube 30, we allow a portion of the coal particles to move downwardly with the impurities. This is accomplished by selecting the amount of suction developed by the pump. This limited amount of coal particles will move downwardly with the impurities below the deflector ring 32 and will enter the outlet passage 14. This mixture will then be supplied to the final separator 12 which will function in a manner similar to the primary separator 11 to remove substan-' tially all the coal particles from the extraneous waste material.

It will be apparent that in the primary separator 11, the mixture not only will be swirled around in the separation chamber 35 because of its introduction therein tangentially under pressure at the upper end of such chamher but also because of the rotation of the tube 30 there within. The bed of materials along the peripheral wall of the chamber 35 will, therefore, be kept mobile leading to better separation. Also, it will not be necessary to add media to create the proper type of bed for separation.

As previously indicated, the final separator 12 is similar in construction and operation to the primary separator 11. The percentage of impurities in the coal mixture supplied to the primary separator 11 is variable, depending upon the coal seam and the mining system employed. The coal and impurities mixture is discharged from the primary separator 11 (FIGURE 1) through the outlet 14 as a heavy stream under pressure, into the final separator 12 and enters the latter at the inlet 13a similar to the manner in which the original mixture enters the primary separator at the inlet 13.

This final separator includes a frusto-conical housing 15a, similar to the housing 15, which carries at its upper end a cylindrical housing 17a, similar to the primary separator housing 17 but of substantially greater vertical extent because it encloses a centrifugal pump of somewhat different form, the pump in this instance having a double impeller 25a. This impeller is carried by a depending shaft 22a which extends downwardly through a packing gland 23a that is mounted on a disc 19a. This disc 1% supports standards 21a which carry bearings for the shaft 22a and certain parts of the shaft driving system like the corresponding structure described in connection with the primary separator 11.

The double impeller 25a consists of an upper disc 26a, an intermediate disc 27a and a lower disc 27b, all spaced vertically and axially. Between the discs 26a and 27a are the blades 2% (FIGURES 1 and 5) of the upper impeller while between the discs 27a and 27b are the blades 2% (FIGURES 1 and 6) of the lower impeller. An inner central suction tube 30a for the upper impeller chamber is carried by the intermediate disc 27a for rotation therewith. A surrounding concentrically spaced suction tube 30b for the lower impeller is carried by the lowermost disc 27b. The lower end of this tube 30b is provided with a collar 31b threaded thereon which cooperates with the adjacent deflector ring 32a on the inner surface of the inverted cone section vhousing 15a. Carried on the extreme lower end of the suction tube 30a is a flared or hell shaped collar 310 which has its outer extremity below the deflector ring 32a. The collar 31a is threaded on the tube 30a so that it will be vertically adjustable thereon and relative to the deflector ring 32a. As a further supporting means for the tube 30a, the collar 31a is carried by a spider 40 which is threaded on the upper end of a hub member 41 which is rotatably carried at its lower end by an upwardly projecting tapered plug 42 that is mounted in the base place 43 of the housing section 15a. Leading from the upper impeller chamber of the centrifugal pump is a tangential discharge passageway 370 (FIGURE 5) which is controlled by a flow regulating valve 44. Leading from the lower impeller chamber of the centrifugal pump is a tangential discharge passageway 37b (FIGURE 6) which is controlled by a flow regulating valve 45.

In this final separator, the outlet 14a, through the bottom plate 43, is restricted and communicates with an auger-type conveyor 46. This conveyor includes a tubular housing which has an upturned elbow-like discharge outlet 47. Within the tube of the conveyor 46 is the screw or auger 48 which is driven by a suitable exterior driving connection 49. A water inlet tube 50 is connected to the screw housing adjacent the outlet 47.

The final separator 12 will function substantially the same as the primary separator, except that it will be even more efiFective to separate the fine particles of coal from the waste material due to the double centrifugal pump arrangement. The inflowing material will again be subjected to centrifugal force as it swirls downwardly through the separator chamber 35a. The bed of material will be formed as before with the higher specific gravity reject impurities collecting against the peripheral wall of the chamber 35a and the lower density coal particles being at the inner side of the downwardly moving bed. Both of the tubes 30a and 30b will serve to keep the bed of material in a constant circular motion. When the materials reach the deflector ring 32a, some of the coal particles will be deflected upwardly into the outer suction tube 3% and will be drawn upwardly through the suction tube by the lower impeller. The bed of reject material and some coal particles will continue to pass on downwardly through the restricted annular space between the deflector ring 32a and the outwardly flared collar 31a. The outwardly sloping or conical shelf provided by the collar 31a will receive the high density material, which may fall out from the material deflected upwardly by the ring 32a, and will be thrown outwardly by centrifugal force toward the lower outward and downard sloping surface of the deflector ring 32a. This high density material with some lighter coal particles will move on downwardly into the chamber 3512 which is similar in shape to the chamber 35a. Here again a similar separation will occur and some of the coal particles will pass upwardly through the spider 40 into the inner suction tube 30a, this action being aided by the rotation of the conical shaped hub 41 and by the suction generated within the tube 3% by the upper impeller. Thus, there are two separate impeller chambers with separate discharges 37a and 371), respectively, for the separated particles which will consist mainly of coal particles. The resulting coal products can, therefore, be kept separate and, if expedient, either one of these products can be piped into the intake 13 of the primary separator 11 for recirculation in order to provide additional high-density material which ultimately allows for the proper extraction of the highdensity material. We have found, by experimenting with this apparatus, that it is advantageous to have a substantial portion of high-density material to complete a satisfactory commercial separation. Each of the separate impellers will produce a predetermined flow but it may be expedient to reduce the upward velocities through the individual tubes 30a and 30b to suit withdrawal of the separated particles at the respective outlets 37a and 371'). Although the shafts 22 and 22a may be driven with variable speed drives to obtain the upward currents most desired, the flow valves 44 and 45 will provide additional means for regulating the flow.

Most of the material which passes through the restricted outlet 14a will be high-density reject particles. However, by supplying water to the conveyor at the bottom of the separator 12 through the inlet tube 50 and because of the agitation created by the rotation of the screw 48, the material will be agitated in the conveyor which will provide an additional separation chamber within the conveyor. The screw 48 will be operated at such a speed that suflicient solid material will build up in the upturned outlet 47 to provide a substantial seal. This will prevent air from the atmosphere from being drawn into the pump and thereby rendering it ineffective. The material within the conveyor chamber will be agitated, as indicated, and any remaining lighter coal particles will rise to the upper surface thereof and because of the inwardly flowing stream created through the inlet tube 50 will be floated back up through the outlet 14a and will be carried from the chamber 3512 up into the inner suction tube 30a. This will augment the flow of water into the central suction tube 30a. This directional flow of water creates additional means for the separation and removal of displaced low density materials which may still be present in the rejects caused by the inconsistency of the materials entering at the intake of the machine, such as intermittent feed, variations in the waterflow and any irregularities encountered. The spiral screw 48 operates in the conveyor housing which is filled with water. The reject materials are pushed toward the outlet 47 while submerged and the pushing action of the spiral or screw keeps this material in a mobile condition. As described previously, this mobility of the bed will force the low density materials upwardly. The water current is regulated to pick up such material and causes it to flow back toward the outlet 14a.

A decided advantage in the separation of materials according to our invention is the downward flow of the water and the materials. It is possible to use a swift flowing current in which the centrifugal gravitational forces are assisting to divide the intermixed materials into high and low density layers. In many coal cleaning devices the materials are subjected to upward current flow in which the low density materials are carried upwards along with the current and in which the high density materials are allowed to sink against the rising current. Devices of this type are limited in capacity in proportion to the allowable velocity of the upward flowing current. This same condition occurs in coal washers using horizontal currents such as those known as the Launder type washers and concentrating tables.

With our invention, the centrifugal force acting on the particles will create a greater differential separating force. The water and materials whirling around at a peripheral speed of about 1,000 feet per minute in a circular path of 8" diameter will generate about 20 times gravity at the outer edge. A coal particle with a specific gravity of 1.4 and submerged in water under such conditions will contain a potential force of 20 .4 or the equivalent of 8 times its weight and accordingly, a high-density particle of 1.45 specific gravity will contain a force of 20 .45 equaling 9 times its weight.

There are additional separating forces with our invention created by the downward velocity of the water and the materials combined with the difference in weight between the low-density and high-density materials; however, no attempt is made to define this advantage. It is easily understood that the various controls incorporated in this machine are of great value to produce a'desired separation.

Our machine is very compact and has a high capacity. Also, we provide a novel pump arrangement with an extended suction pipe fastened to the impeller to bring the suction or intake pointto the level required. Rotation of this pipe is also another important feature. This is essential in this type of separator because it helps maintain the circular movement of the water and the materials to be processed. The friction between the outer wall of the rotating pipe provides a gentle rotating force for the liquid. We found by experimenting that bars or blades on the side of the pipe would disturb the fluid suspension of the rotating mass and thereby disturb the gravitational separation existing in the bed.

The removal of the reject or refuse material is accomplished in a novel manner by the screw or auger type conveyor. In the horizontal screw housing, this material is immersed in water. The screw conveys it toward the elbow or discharge end of the housing. The screw provides a pushing action resulting in squeezing out the water, forming a comparatively air-tight enclosure to prevent air from entering into the pump and also delivering a dry refuse. Air is not permitted to enter the final separator and destroy the suction in the pumps. The removal of the water from the refuse product is of considerable advantage because the material can be readily disposed of in a conveyor or directly into trucks for disposal. In

most processes, the rejects are discharged in a fluid con? dition mixed with water. The water is then removed by means of vibrating screens or other methods of draining, such as drainage elevators or vacuum filters. This removal of water from the refuse is not necessary with our system.

In FIGURE 1, there is shown an extension E, on the left side below the primary separator. This is to indicate that additional primary separators could be connected at this point to the final separator. When coal containing a small percentage of impurities has to be processed, the final separator could receive and process the materials discharged from additional primary machines.

It will be apparent from the above that our invention provides a simple, low-cost yet effective apparatus for separating and classifying particle or granular materials of different specific gravity by the use of centrifugal force and gravity in connection with a media which is created solely from the coal and impurities mixture plus water. It is not necessary to add high specific gravity particles, such as magnetite, to the coal mixture to create the media suitable for separation and classification and, therefore, it is not necessary to subsequently separate this added material.

According to the provisions of the patent statutes, the principles of this invention :have been explained and have been illustrated and described in what is now considered to represent the best embodiment. However, it is to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

Having thus described our invention, what we claim is:

1. Apparatus for separating and classifying fragmentary materials containing particles of different specific gravities, which comprises a separation chamber of inverted conical form having a sloping wall, means for supplying a mixture of the particles in water to the chamber through an inlet at an upper level directed tangentially into said chamber so that the mixture will swirl therein around the axis thereof and simultaneously move downwardly toward an outlet for particles of higher specific gravity at a lower level of said chamber, a centrifugal pump of the double impeller type mounted in cooperation with said chamber, a suction tube for each impeller of the pump mounted for rotation therewith, both of said suction tubes being disposed coaxially in said chamber to provide inner and outer tubes and spaced from each other and depending in said chamber to provide inlet lower ends at a level intermediate said chamber inlet and outlet so as to withdraw upwardly from the chamber the particles of low pecific gravity, said chamber wall converging toward said lower inlet end of said outer tube, a deflector ring a.) on said wall adjacent said lower end of said outer tube for deflecting material from said wall into said tube, the inner suction tube having a lower inlet end extending downwardly to a lower level than the end of the outer tube, said pump having a tangential discharge outlet.

2. Apparatus according to claim 1 in which said inner tube carries an outwardly flared collar on its lower end which extends beneath the lower end of the outer tube adjacent the lower surface of the deflector ring.

3. Apparatus according to claim 2 in which the pump impellers are disposed in separate chambers communicating with the respective suction tubes, each of said chambers having a tangential discharge outlet controlled by a flow valve.

4. Apparatus according to claim 2 in which a rotatable conical member is disposed in the chamber below said flared collar, the outlet for said chamber being located below said member.

5. Apparatus according to claim 4 including an anger type conveyor connected to aid outlet, said conveyor having a housing with an upturned outlet which will fill with particles to substantially seal it.

6. Apparatus according to claim 5 in which the housing is connected at one end to the chamber outlet and has its outlet at the other end, and a water inlet leading into said housing adjacent its outlet end.

7. Apparatus according to claim 5 in which said auger type conveyor includes a tubular housing communicating at one end at its upper side with said outlet, a rotatable screw in the housing for pushing the refuse material toward a remote discharge end, said discharge end communicating with the atmosphere but being turned upwardly above the screw to provide for building up of a body of fragments which will substantially seal that end against inlet of air, and means adjacent-that end for introducing water into the tubular housing to permit it to flow toward said inlet and to be drawn upwardly therethrough by said suction force.

8. Apparatus for separating and classifying fragmentary materials containing particles of different specific gravities, which comprises a separation chamber of inverted conical form having a sloping wall, means for supplying a mixture of the particles in water to the chamber through an inlet at an upper level into said chamber and causing it to swirl downwardly toward an outlet for particles of higher specific gravity at a lower level ofsaid chamber, a centrifugal pump of the multiple impeller type mounted in cooperation with said chamber, a suction tube for each impeller of the pump mounted for rotation therewith, all of said suction tubes being disposed coaxially in said chamber and spaced from each other and depending in said chamber to provide inlet lower ends at a level intermediate said chamber inlet and outlet so as to withdraw upwardly from the chamber the particles of low specific gravity, said chamber wall converging toward said suction tubes, said ends of said tubes being located at successively different lower levels with the end of the outermost tube being the highest to provide multiple selective suction forces, said pump having a discharge for all of said impellers.

References Cited by the Examiner UNITED STATES PATENTS 2,645,346 7/1953 Staege 209- 211 2,645,347 7/1953 Baxter 209 211 2,701,642 2/1955 Goodwin 209 211 2,706,045 4/1955 Large 209 211 2,856,072 10/1958 Kronstad 209 211 2,996,187 8/1961 Payne 209 211 3,172,844 3/1965 Kurz 209 211 3,235,091 2/1966 D011 209 211x FRANK W. LUTTER, Primary Examiner. 

8. APPARATUS FOR SEPARATING AND CLASSIFYING FRAGMENTARY MATERIALS CONTAINING PARTICLES OF DIFFERENT SPECIFIC GRAVITIES, WHICH COMPRISES A SEPARATION CHAMBER OF INVERTED CONICAL FORM HAVING A SLOPING WALL, MEANS FOR SUPPLYING A MIXTURE OF THE PARTICLES IN WATER TO THE CHAMBER THROUGH AN INLET AT AN UPPER LEVEL INTO SAID CHAMBER AND CAUSING IT TO SWIRL DOWNWARDLY TOWARD AN OUTLET FOR PARTICLES OF HIGHER SPECIFIC GRAVITY AT A LOWER LEVEL OF SAID CHAMBER, A CENTRIFUGAL PUMP OF THE MULTIPLE IMPELLER TYPE MOUNTED IN COOPERATION WITH SAID CHAMBER, A SUCTION TUBE FOR EACH IMPELLER OF THE PUMP MOUNTED FOR ROTATION THEREWITH, ALL OF SAID SUCTION TUBES BEING DISPOSED COAXIALLY IN SAID CHAMBER AND SPACED FROM EACH OTHER AND DEPENDING IN SAID CHAMBER TO PROVIDE INLET LOWER ENDS AT A LEVEL INTERMEDIATE SAID CHAMBER INLET AND OUTLET SO AS TO WITHDRAW UPWARDLY FROM THE CHAMBER THE PARTICLES OF LOW SPECIFIC GRAVITY, SAID CHAMBER WALL CONVERGING TOWARD SAID SUCTION TUBES, SAID ENDS OF SAID TUBES BEING LOCATED AT SUCCESSIVELY DIFFERENT LOWER LEVELS WITH THE END OF THE OUTER- 